This invention relates to a transponder that performs bidirectional conversion between a client-side signal and a transmission path-side signal, and more particularly, to a transponder that determines a connection destination of an interface at which the client-side signal is input/output.
In a transmission system (optical transmission system) in which a client device and another client device opposed to the client device are connected to each other through a transmission path, it is necessary to notify the client device of the occurrence of a failure when the failure has occurred in the transmission path or the like.
As one known example, the transmission system includes two terminal equipments connected to two client devices, and the terminal equipments are connected to each other through a transmission path. The terminal equipment includes one transponder that performs bidirectional conversion between a client-side signal used for communication to the client device and a transmission path-side signal used for communication to the transmission path. When a signal is output from the client device, the transponder of the terminal equipment connected to the client device converts a client-side signal into a transmission path-side signal and outputs the converted signal to the transmission path side. On the other hand, when a signal is input to the client device, the transponder converts a transmission path-side signal into a client-side signal and inputs the converted signal to the client device.
Further, one transmission path has a fixed length, and hence, the length of the transmission path can be enlarged by providing at least one repeater between two terminal equipments. This is because two transmission paths are connected to one repeater. The repeater includes two transponders. One of the transponders converts a transmission path-side signal into a client-side signal, and the other converts a client-side signal output from one transponder into a transmission path-side signal.
The transponder includes a client-side interface connected to the client device or the other transponder and a transmission path-side interface connected to the transmission path.
The client-side interface of the transponder provided in the terminal equipment is connected to the client device, and the transmission path-side interface is connected to the transmission path. The client-side interface provided in the repeater is connected to the other transponder, and the transmission path-side interface is connected to the transmission path.
In the following description, the terminal equipment and the repeater are sometimes collectively referred to “communication device”.
As a system of notifying the client device of the occurrence of a failure in the above-mentioned transmission system, there are known a system in which failure information indicating the occurrence of a failure is included in an overhead part of a light signal and a system in which a frame for transferring the failure information is generated and the frame is transferred to the client device.
For example, in the case of the former system, in a synchronous digital hierarchy (SDH) system, a signal called an alarm indication signal (AIS) is included in a frame of a transmission signal flowing through the transmission path, and thus, failure information is transferred to the client device.
Further, in the case of the latter system, in an Ethernet system of the 10-Gigabit Ethernet, a failure transfer function called link fault signaling (LFS) is standardized.
However, in order for a communication device to detect the failure information, it is necessary to decode a light signal at high speed to read a warning signal. Therefore, there is a problem in that the cost for the communication device rises.
In order to lower the cost for the communication device, the following method is known. When a failure has occurred, the output of a light signal is stopped at a client-side interface of a transponder to notify a client device of the occurrence of the failure, and a client loss of signal (LOS) signal that notifies the client device of the occurrence of the failure is output through use of an Ether-OAM signal at a transmission path-side interface (for example, see Japanese Patent Application Laid-open No. 2010-81223).
This method is described with reference to FIGS. 10 to 12.
FIG. 10 is an explanatory diagram of a failure notification method in the case where a failure has occurred in a transmission path in a conventional example.
A transmission system includes a client device 100, a terminal equipment 200, a terminal equipment 500, and a client device 600. The terminal equipments 200 and 500 are connected to each other through a transmission path 440.
The terminal equipment 200 includes a transponder 420 and an optical multiplexer 430. The transponder 420 converts a client-side signal from the client device 100 into a transmission path-side signal. The optical multiplexer 430 multiplexes the transmission path-side signal from the transponder 420 and outputs the resultant signal to the transmission path 440 side.
The terminal equipment 500 includes a transponder 460 and an optical de-multiplexer 450. The optical de-multiplexer 450 de-multiplexes the transmission path-side signal from the transmission path 440 and outputs the resultant signal to the transponder 460. The transponder 460 converts the transmission path-side signal output from the optical de-multiplexer 450 into a client-side signal and outputs the converted client-side signal to the client device 600.
It is assumed that a failure such as the disconnection of an optical fiber has occurred in the transmission path 440 (51). In this case, a light signal does not reach a downstream side from a place where the failure has occurred. Therefore, the transponder 460 provided in the terminal equipment 500 detects an LOS (52) and stops the output from the client-side interface connected to the client device 600 (53). The client device 600 detects the LOS (54) and can detect that some failure has occurred in the transmission system.
FIG. 11 is an explanatory diagram of a failure notification method in the case where a failure has occurred between the client device 100 and the terminal equipment 200 in the conventional example.
The configuration of the transmission system illustrated in FIG. 11 is the same as that of the transmission system illustrated in FIG. 10, and hence, the description thereof is omitted.
When a failure such as the disconnection of an optical fiber has occurred between the client device 100 and the terminal equipment 200 (51), a light signal does not reach a downstream side from a place where the failure has occurred. Therefore, the transponder 420 provided in the terminal equipment 200 detects an LOS (52) and outputs a client LOS signal from the transmission path-side interface to the downstream side (55).
When the client LOS signal from the transponder 420 is input to the transponder 460, the transponder 460 stops the output from the client-side interface connected to the client device 600 (53). The client device 600 detects the LOS (54) and can detect that some failure has occurred in the transmission system.
FIG. 12 is an explanatory diagram of a failure notification method in a multi-stage transmission system of the conventional example.
A transmission system illustrated in FIG. 12 is a multi-stage transmission system which includes two repeaters 300 and 400 (hereinafter, collectively referred to as “repeater 300”) and in which a transmission path is extended. It should be noted that the transmission system including at least one repeater 300 is called a multi-stage transmission system.
Client devices 100 and 600 illustrated in FIG. 12 are the same as the client devices 100 and 600 illustrated in FIG. 10, and terminal equipments 200 and 500 illustrated in FIG. 12 are the same as the terminal equipments 200 and 500 illustrated in FIG. 10, and hence, the descriptions thereof are omitted.
The repeater 300 includes an optical de-multiplexer 640, a transponder 650, a transponder 660, and an optical multiplexer 670.
The optical de-multiplexer 640 is the same as the optical de-multiplexer 450 provided in the terminal equipment 500 illustrated in FIG. 10, and the optical multiplexer 670 is the same as the optical multiplexer 430 provided in the terminal equipment 200 illustrated in FIG. 10, and hence, the descriptions thereof are omitted.
A transmission path-side interface of the transponder 650 is connected to the optical de-multiplexer 640 and a client-side interface of the transponder 650 is connected to the transponder 660. The transponder 650 converts a transmission path-side signal into a client-side signal.
A transmission path-side interface of the transponder 660 is connected to the optical de-multiplexer 670 and a client-side interface of the transponder 660 is connected to the transponder 650. The transponder 660 converts a client-side signal into a transmission path-side signal.
The configuration of the repeater 400 is the same as that of the repeater 300, and hence, the description thereof is omitted.
When a failure such as the disconnection of an optical fiber has occurred between the client device 100 and the terminal equipment 200 (810), a light signal does not reach a downstream side from a place where the failure has occurred. Therefore, the transponder 420 provided in the terminal equipment 200 detects an LOS (820) and outputs a client LOS signal from the transmission path-side interface (830).
When the client LOS signal is input to the transponder 650 provided in the repeater 300, the transponder 650 stops the output of the client-side interface (840).
The transponder 660 detects the LOS based on the stop of the output from the client-side interface by the transponder 650 (850), and outputs a client LOS signal from the transmission path-side interface (860).
When the client LOS signal is input to the transponder 690 provided in the repeater 400, the transponder 690 stops the output of the client-side interface (870).
The transponder 700 detects the LOS based on the stop of the output from the client-side interface by the transponder 690 (880), and outputs a client LOS signal from the transmission path-side interface (890).
When the client LOS signal is input to the transponder 450 provided in the terminal equipment 500, the transponder 450 stops the output of the client-side interface (900).
The client device 600 detects the LOS (910) and can detect that some failure has occurred in the transmission system.
In the multi-stage transmission system illustrated in FIG. 12, an output to a client device is stopped so as to notify the client device of the occurrence of a failure from the viewpoint of using the transponders provided in the terminal equipments 200 and 500 and the transponders provided in the repeaters 300 and 400 in common. Therefore, in all the transponders, when a client LOS signal is input to a transmission path-side interface, the output from the client-side interface is stopped.
Therefore, all the transponders connected to the transmission path output client LOS signals in spite of the fact that a failure has occurred at one place of the client-side interface, and hence, it is difficult for a manager to check all the client LOS signals to identify the failure place.